The present invention relates to a method of actuating a throttling element arranged in the intake system of an aircompressing fuel-injected internal combustion engine.
German Patent document DE-PS 3,128,783, discloses a method of this generic type for controlling exhaust gas recirculation for the purpose of reducing the emission of pollutants, in particular the emission of particulates. In addition, a reduction of the emission of nitrogen oxides (NO.sub.x) can also be achieved by exhaust gas recirculation. The actuation of a butterfly valve arranged in the intake line is there effected stepwise in coordination with an exhaust gas recirculation valve arranged in an exhaust gas recirculation line.
The object of the present invention is to provide a method of actuating a throttling element of this type which achieves a reduction in the emission of pollutants, in particular the emission of particulates and nitrogen oxides, without the use of an expensive device for exhaust gas recirculation.
Improved combustion, and thus reduced emission of pollutants, is in general obtained right into the partial load range by a reduction in the mass flow of intake air by throttling the intake air flow, due to reduced cooling of the combustion chamber. Therefore, the object of the present invention is achieved by a precise matching of the throttling of the intake air to the operating point of the internal combustion engine which, on the one hand selectively reduces the reactants nitrogen and oxygen and, on the other hand selectively increases the ignition delay. This leads to a relatively late release of heat in the combustion chamber under load, thereby reducing the formation of particulates and nitrogen oxides. At the same time, it has only an insignificant effect on the emission of hydrocarbons. In addition, this progression of heating leads to an increased oxidation of the particulates forming at the beginning of the combustion process and hence also to a reduction in the emission of particulates.
In relation to a particular load and speed point, correction of the setpoint value for the absolute pressure in the intake system guarantees uniform, or only partially reduced, differential pressure between the intake system and the atmosphere. The throttling effect is thus made independent of the altitude at which the internal combustion engine is operated, while at the same time, premature emission of blue smoke from the internal combustion engine, is prevented by a complete opening of the butterfly valve below a predetermined limiting value for the atmospheric pressure, i.e., from a certain altitude.
The tendency of engines in this type to emit blue smoke is diminished by a reduction of throttling (increase of the setpoint value for the absolute pressure) in response to lower outside temperatures, and a thermal overloading of the internal combustion engine is at the same time prevented by a reduction of throttling in the direction of higher outside temperatures. Similarly, in the cold-running phase of the internal combustion engine the susceptibility to the emission of blue smoke is reduced and likewise that the internal combustion engine is protected from thermal overloading by the method according to the invention.
Other objects advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.